1. Field of the Invention
This invention relates to a coin-operated symbol-selecting entertainment machine, that is, a machine of the kind which is operated by a player, after actuation by insertion of one or more coins, to play a game involving selection of a combination of symbols, whereby an award is made available in the event that the combination is of a predetermined winning nature.
As used herein the term coin-operated is intended to cover operation by tokens, credit cards or any other form of monetary value or means of establishing game-playing credit.
Coin-operated symbol-selecting machines of the fruit machine or poker machine kind commonly have a number of rotatable reels with symbols around their peripheries. The reels are rotated and are brought to rest with selected symbols displayed through a window on one or more win lines.
The stopping position may be randomly determined by a software routine which involves selection from a list of numbers one for each of the different possible stopping positions of the respective reel.
With this arrangement, considering by way of example three reels each having 24 possible stopping positions, the least likely combination (i.e. three symbols which appear only once on each reel) has odds of 1 in 13824 (24.times.24.times.24). These odds are not small enough for it to be viable to payout a large jackpot win (of say 10,000 game credits) together with regular smaller payouts. A payout of 10,000 credits at odds of 1 in 13824 represents approximately 72% return whereby payouts would have to be very infrequent to retain profitability.
2. Description of the Prior Art
To overcome this limitation, U.S. Pat. No. 448,419 proposes the use of an enlarged `virtual reel` which has more stopping positions than the actual reel. Selection is effected at random from a list of numbers which is greater than the number of stopping positions, at least some of the stopping positions having two or more numbers in the list which correspond. In this way, if the virtual reel (list of numbers) is say twice the size of the actual reel, with three 24 position reels the odds for the least likely combination would be 1 in 110592.
Another proposal is contained in U.S. Pat. No. 4,858,932. Each stopping position for each reel is assigned a group of sub-intervals or a probability factor. Random selection is effected through the sub-intervals or probability factors and there is an increased likelihood that the stopping position selected will be one to which a larger group of sub-intervals or a higher probability factor has been assigned. This is equivalent to the use of an enlarged `virtual reel` in that the stopping positions through which the selection is made are effectively expanded compared with the actual reel.